Gardiner, Alan Henderson (1957), Egyptian grammar being an introduction to the study of hieroglyphs, 3rd, revised edition, page 485
Walsem, René van (2020), Reinterpreting Gardiner, Egyptian Grammar, Sign-List N 5: : "ra": 'sun'. In Weber, Anke, Martina Grünhagen, Lea Rees, and Jan Moje (eds), Akhet neheh: studies in honour of Willem Hovestreydt on occasion of his 75th birthday,, page 14